A device whereby the upper blade is vertically moved by a guide is known as one type of conventional workpiece cutting apparatus. However, with the above-described kind of apparatus whereby the upper blade is moved vertically, the system for vertically moving and guiding the vertical movement of the upper blade becomes complicated and increases the costs.
In order to solve these kinds of problems, an apparatus has been proposed wherein a ram, having an upper blade mounted thereon, is pivoted vertically about a horizontal pivoting support shaft. Accordingly, the vertical movement system of the upper blade is simplified and the cost is decreased.
However, with an apparatus that vertically moves a ram, it is difficult to prevent variation in the clearance between the upper and lower blades.
Hereafter, an explanation of this will be given.
It is necessary to adjust the clearance between the upper and lower blades to a suitable value in response to the thickness of the material of the workpiece to be cut and an adjustment operation is performed when a lot of the material is to be cut through. In U.S. patent appln. Ser. No. 08/897,691, filed Jul. 21, 1997, the present applicant has proposed using an eccentric shaft on the pivoting support shaft, changing the position of the pivot center of the ram by adjusting the angle of pivot of the eccentric shaft and thus, adjusting the clearance as a means for adjustment of the clearance between the upper and lower blades. However, in the previously described apparatus, a minute amount of play is generated at the bearing, which is arranged between the pivoting support shaft (i.e., the eccentric shaft) and the ram, so that the bearing rigidity is insufficient and variation is generated in the clearance between the upper and lower blades. As the upper and lower blades on the right angle shear are relatively long, the slight amount of play and the lack of rigidity in the bearing leads to variation in the clearance. This variation can be reduced by applying pressure to the bearing, but resistance to the operations performed, when clearance adjustment is carried out due to rotation of the eccentric shaft, is generated, while the pressurized state, and thus, the adjustment operation is difficult to perform.